1. Field of the Invention
The present invention relates to the data sort technology of ordering records by comparing the values of the records corresponding to items specified as sort keys in a large amount of record data constructing a large number of records comprising a plurality of items, and more specifically to the data sort technology of character string data having a record structure in CSV (Comma Separated Value) format data and text format data such as an XML (Extensible Markup Language) document.
2. Description of the Related Art
Conventionally, data sort methods can be selection sort, insertion sort, bubble sort, Shell sort, quick sorts, etc. In these methods, a record, which is a unit for a sort, is compared individually. Therefore, it is necessary to repeatedly read the same records each time a sorting process is performed, and the time required to perform the sorting process increases in progression with an increasing number of records. Normally, assuming that the number of records is n, the time required to perform a sorting process in each method can be expressed by the following equation.
Simple selection method: n to the 2nd power
quick sort: n log n˜n to the 2nd power
insertion sort: n to the 2nd power                (in case of a large number of records)        
bubble sort: n˜n to the 2nd power
Shell sort: n to the 1.5th power˜n to the 1.25th power
Thus, in the conventional data sort methods, the time required to perform the process of sorting a large amount of record data increases in progression with an increasing number of records, thereby causing the problem that the integrity and servability of data can be badly damaged.